What Does Your Building Project Really Cost
Realistic cost estimates for extensions, loft conversions, renovations, new builds and energy installations across London and the UK. Based on real 2026 market data — not marketing figures.
Get an Instant Building Cost Estimate
Enter your postcode and select the work you’re planning. Independent, data-driven estimates — not a quote, and not tied to any single contractor.
Required for planning applications, structural changes and most extensions over 40 m². Includes drawings, planning application coordination and design management.
Indicative estimates only. Always obtain written quotes from qualified contractors.
Why Building Costs Are So Hard to Budget
Most homeowners start with a number in their head — and end up spending 30–50% more than they planned.
The reason isn’t dishonest contractors. It’s that building costs are genuinely complex — and most online cost guides show minimum figures, not realistic ones.
A kitchen renovation is not £8,000. A loft conversion is not £25,000. A house extension in London is not £35,000.
These figures appear everywhere online. They reflect the cheapest possible outcome under ideal conditions. They do not reflect what most people actually pay.
FairBuildCost.co.uk shows you what building work actually costs — with VAT included, contingency included, compliance costs included, and London zone premiums applied correctly.
Four Honest Price Levels — Not One Misleading Average
Every project on this platform is priced across four specification levels. You choose the one that matches your project.
| Level | Who It’s For |
|---|---|
| Budget | Rental properties, fast turnaround, cost-first decisions. Entry-level materials, local contractors. Contingency: 10% |
| Standard | Most homeowners. Mid-market materials, experienced contractors, solid finish. Contingency: 15% |
| Premium | Owner-occupiers wanting quality finish. High-spec materials, specialist contractors. Contingency: 20% |
| Luxury | High-value London properties. Architect-led, bespoke, fully project managed. Contingency: 25% |
Every price level includes: labour + materials + compliance + VAT + contingency.
Cost Guides for Every Type of Building Work
Extensions — Single storey · Double storey · Side return · Wrap-around · Garage conversion
Loft Conversions — Velux · Dormer · Hip to Gable · Mansard
Renovation & Refurbishment — Full house · Kitchen · Bathroom · En-suite · Structural alterations
Basement & New Build — Basement conversion · Basement excavation
Energy Installations (DEH & P LTD) — Heat pump · Solar PV · Battery storage · Air conditioning · MVHR · EV charger
Maintenance & Compliance — Roof replacement · Damp proofing · External wall insulation · Windows · Rewire
London Building Costs by Zone
Building work in London costs significantly more than the UK average — and varies substantially between zones.
| Zone | Areas | Cost vs UK Average |
|---|---|---|
| Zone 1–2 | Mayfair, Chelsea, Kensington, Westminster, City | +50–65% |
| Zone 3–4 | Clapham, Fulham, Hackney, Islington, Battersea | +35–45% |
| Zone 5–6 | Croydon, Barnet, Bromley, Harrow, Enfield | +15–25% |
| South East | Surrey, Kent, Hertfordshire, Berkshire | +10–15% |
| UK Average | Midlands, North, South West, Scotland, Wales | baseline |
How FairBuildCost Works
Step 1 — Select your work type. Choose from the full list of building, renovation and energy work types.
Step 2 — Enter your postcode. We apply the correct London zone or regional multiplier automatically.
Step 3 — Get four price levels. Budget, Standard, Premium and Luxury estimates with full cost breakdown.
Step 4 — Understand what’s included. Every estimate shows what’s included, what’s not, and what permissions you need.
How Building Work Affects Your Property Value
Understanding what you’ll spend is only half the picture. Understanding what you’ll gain is equally important.
FairBuildCost includes property value impact data for every major work type — based on Land Registry sold price data and EPC register analysis.
| Work Type | Typical Value Added (London Z3–4) |
|---|---|
| Single storey extension | +£60,000–£90,000 |
| Dormer loft conversion | +£75,000–£112,500 |
| Full house renovation | +£75,000–£135,000 |
| Air source heat pump | +£7,500–£22,500 |
| Solar PV + battery | +£7,500–£15,000 |
Energy Installations — Featured Specialist: DEH & P LTD
For heat pump, solar PV, air conditioning and battery storage installations, FairBuildCost features DEH & P LTD as its recommended energy specialist.
DEH & P LTD — MCS certified energy installation specialists. Covering Surrey, London and the South East. Heat pumps · Solar PV · Air conditioning · Battery storage
Key facts:
- Heat pump installations qualify for 0% VAT
- BUS Grant: £7,500 available for air source and ground source heat pumps
- All DEH & P installations are MCS certified
- DEH & P manages your BUS grant application
Get a heat pump or solar quote from DEH & P → dehp.uk
Why Trust These Figures?
Based on real data — not industry averages. Cost data is sourced from EPC register, Land Registry, ONS construction indices, MCS register and DEH & P real project costs.
Updated quarterly. Every cost guide is reviewed and updated every three months. Each page shows the last review date.
VAT always stated. Every figure on this platform states clearly whether VAT is included or excluded. All standard estimates include VAT at 20%. Heat pumps and solar PV at 0%.
No inflated estimates — no misleading minimums. We show what building work actually costs in 2026 — not what it costs in perfect conditions.
Independent platform. FairBuildCost.co.uk is an independent cost information platform. DEH & P LTD is featured for energy work only — not as a general contractor for all building types.
All figures published on FairBuildCost.co.uk are indicative estimates for budgeting purposes only. Actual costs depend on site conditions, structural survey results, planning requirements, specification and contractor pricing. FairBuildCost.co.uk does not provide quotes, does not guarantee costs and is not a contractor. Always obtain at least three written quotes from qualified, insured contractors before committing to any building project. Costs last reviewed: June 2026. Next review: September 2026.